San Francisco grabbed the mantle of ‘greenest’ major city in the US and Canada Green City Index , with New York, Seattle, Denver and Boston rounding out the top five U.S. cities. The study, conducted by the Economist Intelligence Unit (EIU) and commissioned by Siemens assesses and compares 27 major U.S. and Canadian cities on environmental performance and policies across nine categories – CO2 emissions, energy, land use, buildings, transport, water, waste, air quality and environmental governance.